The high-voltage test has the purpose of simulating transient over-voltages in three-phase current mains by means of artificially generated pulselike surges. In that case, distinction is conventionally made between external over-voltages, which are produced by, for example, a lightning strike, and internal circuit over-voltages that arise due to switching processes in the mains. The multiplicity of over-voltage phenomena are, for test purposes, reduced to standardized lightning and circuit surge voltages. For these test voltages characteristic magnitudes are established that describe the rise in the voltage, the peak value and the decay within specific tolerances. In the case of cut-off lightning strike voltage, which is to simulate the effect of very rapid voltage changes, the cut-off time is added as a further characterizing magnitude. The requirements, forms of voltage and the determination of the parameters thereof are defined in ICE 60060-1. Depending on the respective standard check carried out, the high-voltage pulse test system comprises for that purpose a pulse generator and auxiliary components such as a cut-off spark gap, a voltage divider and an overshoot compensator.
In order to generate the required pulse-shaped surge voltages Marx multiplication circuits, also termed Marx generators, in particular have become established on the market in the course of time. The circuit type developed by the inventor of the same name in 1923 and granted as a patent under the number DE 455 933 has been constructed in multiple circuit stages, wherein each of the stages comprises a surge capacitance and a switching element, particularly a switching spark gap, connected in series and a resistor connected in parallel with the surge capacitance and the switching element as well as a resistor connected in series therewith. In that case two successive stages are connected together in such a manner that they are chargeable in parallel and dischargeable in series.
The surge capacitors are charged by means of a charging direct voltage. Interpolated charge resistors in this regard not only limit the charging current, but also allow a transient serial connection of the capacitors by means of the spark gaps. The clearances of the spark gaps are so selected that these are not quite broken down when the maximum charging voltage is reached.
After all surge capacitors have been charged to their quasi-static final value of the voltage, ignition of the lowermost spark gap takes place, which thereupon breaks down. At the next spark gap twice the charging voltage is now present so that this is reliably ignited. Regardless of the number of incorporated stages, the discharging process continues on the basis of addition of the charging voltages of previously ignited stages up to the last stage.
In this manner, surge voltage pulses of very short duration and at the same time large amplitude can be generated, such pulses being particularly suitable for checking purposes and tests in high-voltage engineering and for proving insulation co-ordination and interference resistor in electromagnetic compatibility.
In addition, it is known from, for example DE 196 39 023 [U.S. Pat. No. 6,211,683] to increase the limit load capacitance of the just-described Marx generator by means of a circuit addition in that during the overshoot at the load capacitance i.e. at the test piece, a voltage reduction is achieved that after the overshoot has diminished is increased again. The circuit addition, also termed serial overshoot compensator, thus does not reduce the cause of the overshoot, but provides compensation for the overshoot at the load capacitance, i.e. in particular at the test piece. The overshoot compensator consists of a compensation capacitance and at least one discharge resistor connected in parallel therewith or a discharge spark gap, wherein the circuit addition is to be incorporated in the Marx multiplication circuits in serial mode of construction with respect to the test object. Apart from the overshoot compensator connected in series with the test object, it is also known to design this in a form connected in parallel with the test piece. In departure from the just-described form, in the case of an overshoot compensator constructed in that manner the compensation capacitance and the at least one discharge resistor or discharge spark gap are arranged in series.
Moreover, it is also necessary for simulation of an over-voltage load in accordance with operation and for proving the insulation integrity of high-voltage components to load the test objects, as already mentioned, with a cut-off surge pulse voltage. For a successful devolution of a standard check of that kind it is essential for the applied voltage to be interrupted within a tolerance of a few microseconds of the desired time elapsed since the start of the voltage wave. In technical terms this is realized by cut-off spark gaps such as have been known for a long time from the prior art, for example from DD 143 130.
Moreover, in a high-voltage pulse test system, apart from the test object a capacitively damped pulse voltage divider is also connected with the last stage of the Marx multiplication circuit and reduces the lightning pulse voltage, which is generated on discharge of the stages, to values that can be processed by the measuring and recording instruments.
All these incorporated system components of the high-voltage pulse test system have an appreciable physical size and have to be arranged in the test field at a predetermined mutual minimum spacing dependent on the voltage level. Beyond that, similarly defined voltage-dependent minimum spacings between voltage-carrying elements and the test field boundary have to be maintained. The requirement for space of the entire high-voltage pulse test system is thus substantial. Moreover, in the case of many transformer manufacturers the entire high-voltage pulse test system has to be shifted for changing the test object. In this case the Marx generator and the three further auxiliary components have to be individually moved through the test establishment and reassembled and set up again as a high-voltage pulse test system. This process is time-consuming and inconvenient in practice.